CAPTURE ZONE ANALYSIS OF A SHALLOW-AQUIFER IRRIGATION WELL IN MCHENRY COUNTY, ILLINOIS

A groundwater flow model was developed to understand local groundwater flow systems impacted by an irrigation well within a shallow unconfined aquifer in McHenry County, Illinois. Municipal and domestic water supplies in the county are extracted exclusively from groundwater and largely from shallow sand and gravel aquifers. Thus, the county has taken an aggressive approach to understanding these shallow aquifer systems though regional mapping and flow models. The shallowest, unconfined aquifers, from which many irrigation wells extract groundwater, are comprised of sand and gravel that fill former glacial outwash valleys. A local groundwater flow model was constructed to address the potential impacts of drawdown on groundwater quality and stream discharge. Calibration data include time-dependent head measurements and 2-D geophysical surveys. This model can be used as a tool to determine current impacts of pumping on shallow aquifer systems and to estimate long-term effects.